The invention relates to a method for producing a cast strip with material properties the can be adjusted across the strip cross section and the strip length and a device for carrying out the method.
The hotly contested automobile market forces manufacturers to constantly seek solution for lowering the fleet consumption while at the same time maintaining a highest possible comfort and occupant protection. In this context, weight saving plays an important role, on the other hand also properties of the individual components that promote the passive safety of the passengers during high static and dynamic stresses during operation and in case of a crash.
The pre-material manufactures seek to account for these requirements by providing stress-optimized steel sheets and steel strips (for example Tailor welded or Tailored rolled strips), whose sheet thickness is optimized according to the expected stresses or consist of materials with different strengths.
Such steel sheets and steel strips have to meet relatively high standards regarding strength ductility, tenacity energy absorption, wear and their processability such as for example cold forming, welding and/or surface treatment.
Disadvantages of stress-optimized steel sheets in the welded sheet metal blanks are the laborious cutting and joining processes as well as sharp property gradients at material transition.
A method for producing a composite material from steel is known for example from DE 101 24 594 A1. Here, a ferritic core strip which is directly cast according to the two-roll method is cladded with an austenitic or high alloyed ferritic cladding strip.
In a comparable method according to WO 02/45885 A1 a re-oxidation preventing coating is applied on one or both sides during passage through the rolls.
Disadvantageous in this case is also the sharp jump of the properties of the composite material as a result of the cladding which makes the optimal adjustment of the properties across the strip width according to the respective requirement difficult. Further, the properties cannot be varied across the strip width.
A method for producing strips from lightweight steel by means of a horizontal strip casting system is for example known from the periodical Steel Research 74 (2003), No 11/12, page 724-731. In this method, melt is applied from an application system from a delivery container via a casting groove onto a circulating strip of a horizontal strip casting system. As a result of intensive cooling of the cast strip the applied melt solidifies to a pre strip with a thickness in the range between 6-20 mm. After the complete solidification the pre strip is subjected to a hot rolling process.
With this method, lightweight steel with high manganese or high aluminum content can be ideally produced which are difficult to produce by means of conventional methods such as the continuous casting.
In these lightweight steels a weight reduction which is advantageous for the automobile industry is achieved due to the high proportion of alloy components with a specific weight of far below the specific weight of iron (for example Mn, Si, Al), while at the same time retaining the previous construction method.
So far, it was not possible however to produce steel strips with these known strip casting methods which have material properties which are stress-optimized across the strip cross section and the strip length regarding deformation, crash or wear characteristics.